This invention relates to methods for forming a conductive pattern using photographic film.
A multitude of techniques for shaping (such as stamping, grinding, and milling) and joining (such as welding and mechanical joining) metals are highly developed for the fabrication of macroscopic structures. Application of these techniques to the fabrication and assembly of metallic microstructures (structures having features  less than 100 xcexcm) becomes increasingly difficult as the feature sizes become smaller. For that reason, new approaches to microfabrication that are not derived from fabrication techniques used on a large scale have been developed. A widely used technique for fabrication of metallic microstructures is microelectrodeposition of metals on an appropriately shaped mandrel or template. Two examples of this class of processes are through-mask electroplating and LIGA (Lithographie, Galvanoformung, Abformung), both of which are based on projection photolithography (for LIGA, commonly carried out using x-rays, although the availability of the SU-8 class of photoresist has reduced the need for x-ray exposure in making thick structures). Although these methods provide ways to form metallic microstructures, they are processes with several steps, and require facilities of limited availability.
Recently, methods for the microfabrication of metallic, 2D and 3D structures based on the combination of soft lithography and microelectrodeposition have been described, the latter both through a mask of photoresist and onto patterned, conducting surfaces. The pattern-transfer step in these soft lithographic techniques typically uses an elastomeric stamp with a surface relief structure that carries the desired pattern. These stamps are usually formed by molding polydimethylsiloxane (PDMS) against a xe2x80x98masterxe2x80x99 composed of a relief pattern in photoresist, and obtained by photolithography. These masters may be generated using a technique based on high-resolution commercial printing and high-resolution optical reduction. This procedure is efficient: from design, through stamp, to initial structure typically requires no more than 24 hours. Both the preparation of the mask and the generation of the master by photolithography may require access to specialized devices and facilities (i.e., high-resolution image setters, clean rooms) that are more readily available than the mask-making facilities required in high-resolution photolithography, but that are still not available to every laboratory that might benefit from medium resolution microfabrication.
The present invention provides a method for producing metallic and other conductive microstructures. The microstructures may be produced on a substrate, for example, a planar substrate such as photographic film, and may subsequently be removed from the substrate. The microstructures may be produced in a short amount of time and may use equipment readily available to those skilled in the art.
In one aspect, a method is provided in which a conductive pattern is formed. An article including a metal atom precursor capable of conversion to elemental metal is provided and a first portion of the article is disproportionately exposed to electromagnetic radiation at a level greater than at a second portion of the article. The article is exposed in an amount and for a period of time sufficient to convert at least some of the precursor at one of the portions to elemental metal at a conversion level greater than conversion of precursor to elemental metal at the other portion. Then, a metal is deposited from a source external of the metal atom precursor, proximate the portion of the article including metal atom precursor converted at a greater conversion level in an amount greater than deposition of metal at the other portion.
In another aspect, the invention provides for a method that includes deforming a flexible metal structure from a first configuration to a second configuration and depositing auxiliary metal on the metal structure to the extent that the structure is self-supporting in the second configuration.
In another aspect, the invention provides for a method that includes exposing photoresist to electromagnetic radiation through a metal mask, developing the photoresist to form a photoresist pattern, directing a metal deposition composition to the metal mask via the photoresist pattern, and depositing auxiliary metal on the metal mask.
In another aspect, the invention provides for a method of forming a conductive pattern. A photographic film is illuminated with a desired illumination configuration, and the film is developed so that illuminated or non-illuminated portions of the film are adjusted to be in an altered state. Additional conductive material is selectively deposited onto portions of the film in an altered state in amounts greater than amounts of conductive material deposited on portions of the film not in the altered state.
In another aspect, the invention provides for a method of forming a discontinuous metallic structure. A photographic film is illuminated with a desired structure configuration and the film is developed so that illuminated or non-illuminated portions of the film are adjusted to be in an altered state. Additional conductive material is selectively deposited onto portions of the film in an altered state in amounts greater than amounts of conductive material deposited on portions of the film not in the altered state.
Other advantages, novel features, and objects of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings, which are schematic and which are not intended to be drawn to scale. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention.